High reliability transmission mode for 2-step secondary cell beam failure recovery procedure

ABSTRACT

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for performing beam failure recovery involving a secondary cell.

PRIORITY CLAIM(S)

This application claims benefit of the priority to U.S. ProvisionalApplication No. 62/914,365, filed on Oct. 11, 2019, which is expresslyincorporated by reference in its entirety as if fully set forth belowand for all applicable purposes.

BACKGROUND Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for performing beam failure recoveryinvolving a secondary cell.

Description of Related Art

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,broadcasts, etc. These wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, etc.). Examples of such multiple-access systems include3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)systems, LTE Advanced (LTE-A) systems, code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. New radio (e.g., 5G NR) is an exampleof an emerging telecommunication standard. NR is a set of enhancementsto the LTE mobile standard promulgated by 3GPP. NR is designed to bettersupport mobile broadband Internet access by improving spectralefficiency, lowering costs, improving services, making use of newspectrum, and better integrating with other open standards using OFDMAwith a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL).To these ends, NR supports beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR and LTEtechnology. Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims that follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvingreliability of beam recovery messaging.

Certain aspects of the present disclosure provide a method for wirelesscommunication by a user equipment (UE). The method generally includesperforming beam failure detection (BFD) of a beam pair link (BPL)associated with a secondary cell (SCell) in carrier aggregation (CA),sending a beam failure recovery request (BFRQ) message to another cell,the BFRQ message including an indication of a candidate recovery beamfor the SCell, receiving a message from the other cell, and sending amedia access control (MAC) control element (CE) after receiving themessage, wherein the MAC CE is sent using one or more mechanisms toenhance reliability.

Certain aspects of the present disclosure are directed to an apparatusfor wireless communication by a UE. The apparatus generally includes amemory and at least one processor coupled to the memory, the memory andthe at least one processor being configured to perform beam BFD of a BPLassociated with a SCell in CA, send a BFRQ message to another cell, theBFRQ message including an indication of a candidate recovery beam forthe SCell, receive a message from the other cell, and send a MAC CEafter receiving the message, wherein the MAC CE is sent using one ormore mechanisms to enhance reliability.

Certain aspects of the present disclosure are directed to an apparatusfor wireless communication by a UE. The apparatus generally includesmeans for performing beam BFD of a BPL associated with a SCell in CA,means for sending a BFRQ message to another cell, the BFRQ messageincluding an indication of a candidate recovery beam for the SCell,means for receiving a message from the other cell, and means for sendinga MAC CE after receiving the message, wherein the MAC CE is sent usingone or more mechanisms to enhance reliability.

Certain aspects of the present disclosure are directed to a computerreadable medium having instructions stored thereon for performing beamBFD of a BPL associated with a SCell in CA, sending a BFRQ message toanother cell, the BFRQ message including an indication of a candidaterecovery beam for the SCell, receiving a message from the other cell,and sending a MAC CE after receiving the message, wherein the MAC CE issent using one or more mechanisms to enhance reliability.

Certain aspects of the present disclosure provide a method for wirelesscommunication by a network entity. The method generally includesreceiving a BFRQ message from a UE, the BFRQ message indicating a beamfailure detected in a SCell and including an indication of a candidaterecovery beam for the SCell, and sending a message to the UE, andreceiving a MAC CE after sending the message, wherein the MAC CE is sentusing one or more mechanisms to enhance reliability.

Certain aspects of the present disclosure are directed to an apparatusfor wireless communication by a UE. The apparatus generally includes amemory and at least one processor coupled to the memory, the memory andthe at least one processor being configured to receive a BFRQ messagefrom a UE, the BFRQ message indicating a beam failure detected in aSCell and including an indication of a candidate recovery beam for theSCell, send a message to the UE, and receive a media access control MACCE after sending the message, wherein the MAC CE is sent using one ormore mechanisms to enhance reliability.

Certain aspects of the present disclosure are directed to an apparatusfor wireless communication by a UE. The apparatus generally includesmeans for receiving a BFRQ message from a UE, the BFRQ messageindicating a beam failure detected in a SCell and including anindication of a candidate recovery beam for the SCell, means for sendinga message to the UE, and means for receiving a media access control MACCE after sending the message, wherein the MAC CE is sent using one ormore mechanisms to enhance reliability.

Certain aspects of the present disclosure are directed to a computerreadable medium having instructions stored thereon for receiving a BFRQmessage from a UE, the BFRQ message indicating a beam failure detectedin a SCell and including an indication of a candidate recovery beam forthe SCell, sending a message to the UE, and receiving a media accesscontrol MAC CE after sending the message, wherein the MAC CE is sentusing one or more mechanisms to enhance reliability.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe appended drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the drawings. It is to be noted, however, thatthe appended drawings illustrate only certain typical aspects of thisdisclosure and are therefore not to be considered limiting of its scope,for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram conceptually illustrating a design of anexample a base station (BS) and user equipment (UE), in accordance withcertain aspects of the present disclosure.

FIG. 3 is an example beam failure detection and recovery procedure thatmay be enhanced, in accordance with certain aspects of the presentdisclosure.

FIG. 4 illustrates example operations for wireless communication by aUE, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates example operations for wireless communication by anetwork entity, in accordance with certain aspects of the presentdisclosure.

FIG. 6 is an example beam failure detection and recovery procedure, inaccordance with certain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for performing beam failure recoveryinvolving a secondary cell. In some cases, one or more mechanisms may beutilized to increase reliability of BFR mechanism, implicitly providinghigher priority for the recovery messaging. Examples of such mechanismsinclude beam sweeping and repetition.

The following description provides examples of aspects of the presentdisclosure, and is not limiting of the scope, applicability, or examplesset forth in the claims. Changes may be made in the function andarrangement of elements discussed without departing from the scope ofthe disclosure. Various examples may omit, substitute, or add variousprocedures or components as appropriate. For instance, the methodsdescribed may be performed in an order different from that described,and various steps may be added, omitted, or combined. Also, featuresdescribed with respect to some examples may be combined in some otherexamples. For example, an apparatus may be implemented or a method maybe practiced using any number of the aspects set forth herein. Inaddition, the scope of the disclosure is intended to cover such anapparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to, or otherthan, the various aspects of the disclosure set forth herein. It shouldbe understood that any aspect of the disclosure disclosed herein may beembodied by one or more elements of a claim. The word “exemplary” isused herein to mean “serving as an example, instance, or illustration.”Any aspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, a subband, etc. Each frequency may support asingle RAT in a given geographic area in order to avoid interferencebetween wireless networks of different RATs.

The techniques described herein may be used for various wirelessnetworks and radio technologies me. For clarity, while aspects may bedescribed herein using terminology commonly associated with 3G, 4G,and/or new radio (e.g., 5G NR) wireless technologies, aspects of thepresent disclosure can be applied in other generation-basedcommunication systems.

NR access may support various wireless communication services, such asenhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHzor beyond), millimeter wave (mmW) targeting high carrier frequency(e.g., 25 GHz or beyond), massive machine type communications MTC (mMTC)targeting non-backward compatible MTC techniques, and/or missioncritical targeting ultra-reliable low-latency communications (URLLC).These services may include latency and reliability requirements. Theseservices may also have different transmission time intervals (TTI) tomeet respective quality of service (QoS) requirements. In addition,these services may co-exist in the same subframe.

Certain wireless networks utilize orthogonal frequency divisionmultiplexing (OFDM) on the downlink and single-carrier frequencydivision multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partitionthe system bandwidth into multiple (K) orthogonal subcarriers, which arealso commonly referred to as tones, bins, etc. Each subcarrier may bemodulated with data. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. The systembandwidth may also be partitioned into subbands.

5G NR may utilize OFDM with a cyclic prefix (CP) on the uplink anddownlink and include support for half-duplex operation using timedivision duplexing (TDD). A subframe can be 1 ms, but the basictransmission time interval (TTI) may be referred to as a slot. Asubframe contains a variable number of slots (e.g., 1, 2, 4, 8, 16, . .. slots) depending on the subcarrier spacing (SCS). The NR resourceblock (RB) may be 12 consecutive frequency subcarriers. NR may support abase SCS of 15 KHz and other subcarrier spacing may be defined withrespect to the base SCS, for example, 30 kHz, 60 kHz, 120 kHz, 240 kHz,etc. The symbol and slot lengths scale with the SCS. The CP length alsodepends on the SCS. 5G NR may also support beamforming and beamdirection may be dynamically configured. Multiple-input multiple-output(MIMO) transmissions with precoding may also be supported. In someexamples, MIMO configurations in the DL may support up to 8 transmitantennas with multi-layer DL transmissions up to 8 streams and up to 2streams per UE. In some examples, multi-layer transmissions with up to 2streams per UE may be supported. Aggregation of multiple cells may besupported with up to 8 serving cells.

FIG. 1 illustrates an example wireless communication network 100 inwhich aspects of the present disclosure may be performed. For a UE 120of the network 100 may have a beam failure recovery module 122configured to perform operations 400 of FIG. 4 and/or a BS 110 of thenetwork 100 may have a beam failure recovery module 112 configured toperform operations 500 of FIG. 5.

As illustrated in FIG. 1, the wireless communication network 100 mayinclude a number of base stations (BSs) 110 a-z (each also individuallyreferred to herein as BS 110 or collectively as BSs 110) and othernetwork entities. A BS 110 may provide communication coverage for aparticular geographic area, sometimes referred to as a “cell”, which maybe stationary or may move according to the location of a mobile BS 110.In some examples, the BSs 110 may be interconnected to one anotherand/or to one or more other BSs or network nodes (not shown) in wirelesscommunication network 100 through various types of backhaul interfaces(e.g., a direct physical connection, a wireless connection, a virtualnetwork, or the like) using any suitable transport network. In theexample shown in FIG. 1, the BSs 110 a, 110 b and 110 c may be macro BSsfor the macro cells 102 a, 102 b and 102 c, respectively. The BS 110 xmay be a pico BS for a pico cell 102 x. The BSs 110 y and 110 z may befemto BSs for the femto cells 102 y and 102 z, respectively. A BS maysupport one or multiple cells. The BSs 110 communicate with userequipment (UEs) 120 a-y (each also individually referred to herein as UE120 or collectively as UEs 120) in the wireless communication network100. The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughoutthe wireless communication network 100, and each UE 120 may bestationary or mobile.

Wireless communication network 100 may also include relay stations(e.g., relay station 110 r), also referred to as relays or the like,that receive a transmission of data and/or other information from anupstream station (e.g., a BS 110 a or a UE 120 r) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE 120 or a BS 110), or that relays transmissionsbetween UEs 120, to facilitate communication between devices.

A network controller 130 may couple to a set of BSs 110 and providecoordination and control for these BSs 110. The network controller 130may communicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another (e.g., directly or indirectly) via wirelessor wireline backhaul.

FIG. 2 illustrates example components of BS 110 a and UE 120 a (e.g., inthe wireless communication network 100 of FIG. 1), which may be used toimplement aspects of the present disclosure.

At the BS 110 a, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the physical broadcast channel (PBCH),physical control format indicator channel (PCFICH), physical hybrid ARQindicator channel (PHICH), physical downlink control channel (PDCCH),group common PDCCH (GC PDCCH), etc. The data may be for the physicaldownlink shared channel (PDSCH), etc. A medium access control(MAC)-control element (MAC-CE) is a MAC layer communication structurethat may be used for control command exchange between wireless nodes.For example, a base station may transmit a MAC CE to a user-equipment(UE) to put the UE into a discontinuous reception (DRX) mode to reducethe UE's power consumption. The MAC-CE may be carried in a sharedchannel such as a physical downlink shared channel (PDSCH), a physicaluplink shared channel (PUSCH), or a physical sidelink shared channel. AnMAC-CE may also be used to communicate information that facilitatescommunication, such as information regarding buffer status and availablepower headroom.

The processor 220 may process (e.g., encode and symbol map) the data andcontrol information to obtain data symbols and control symbols,respectively. The transmit processor 220 may also generate referencesymbols, such as for the primary synchronization signal (PSS), secondarysynchronization signal (SSS), and cell-specific reference signal (CRS).A transmit (TX) multiple-input multiple-output (MIMO) processor 230 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, and/or the reference symbols, if applicable, and mayprovide output symbol streams to the modulators (MODs) 232 a-232 t. Eachmodulator 232 may process a respective output symbol stream (e.g., forOFDM, etc.) to obtain an output sample stream. Each modulator mayfurther process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal.Downlink signals from modulators 232 a-232 t may be transmitted via theantennas 234 a-234 t, respectively.

At the UE 120 a, the antennas 252 a-252 r may receive the downlinksignals from the BS 110 a and may provide received signals to thedemodulators (DEMODs) in transceivers 254 a-254 r, respectively. Eachdemodulator 254 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator may further process the input samples (e.g., for OFDM, etc.)to obtain received symbols. A MIMO detector 256 may obtain receivedsymbols from all the demodulators 254 a-254 r, perform MIMO detection onthe received symbols if applicable, and provide detected symbols. Areceive processor 258 may process (e.g., demodulate, deinterleave, anddecode) the detected symbols, provide decoded data for the UE 120 a to adata sink 260, and provide decoded control information to acontroller/processor 280.

On the uplink, at UE 120 a, a transmit processor 264 may receive andprocess data (e.g., for the physical uplink shared channel (PUSCH)) froma data source 262 and control information (e.g., for the physical uplinkcontrol channel (PUCCH) from the controller/processor 280. The transmitprocessor 264 may also generate reference symbols for a reference signal(e.g., for the sounding reference signal (SRS)). The symbols from thetransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by the demodulators in transceivers 254a-254 r (e.g., for SC-FDM, etc.), and transmitted to the BS 110 a. Atthe BS 110 a, the uplink signals from the UE 120 a may be received bythe antennas 234, processed by the modulators 232, detected by a MIMOdetector 236 if applicable, and further processed by a receive processor238 to obtain decoded data and control information sent by the UE 120 a.The receive processor 238 may provide the decoded data to a data sink239 and the decoded control information to the controller/processor 240.

The memories 242 and 282 may store data and program codes for BS 110 aand UE 120 a, respectively. A scheduler 244 may schedule UEs for datatransmission on the downlink and/or uplink.

The controller/processor 280 and/or other processors and modules at theUE 120 a may perform or direct the execution of processes for thetechniques described herein. For example, as shown in FIG. 2, thecontroller/processor 240 of the BS 110 a has a beam failure recoverymodule 241 that may be configured to perform operations 500 of FIG. 5.As shown in FIG. 2, the controller/processor 280 of the UE 120 a has abeam failure recovery module 281 that may be configured to performoperations 400 of FIG. 4, according to aspects described herein.Although shown at the controller/processor, other components of the UE120 a and BS 110 a may be used to perform the operations describedherein.

Certain systems, such as NR, support carrier aggregation (CA). With CA,the UE can use multiple carriers/cells to communicate with a BS (ormultiple BSs). CA involves a primary cell (PCell) and at least onesecondary cell (SCell). An SCell may configured for downlink only, orconfigured for both uplink and downlink. The PCell and SCell(s) can bein different frequency bands, such as a PCell in one frequency range(e.g., FR1, sub-6 GHz) and the SCell in another frequency range (FR2, 28GHz). The PCell and SCell may use different tone spacing or subcarrierspacing (SCS), leading to different symbol lengths for the PCell andSCell(s). For example, in the F1 the symbols length for a 120 KHz SCS iseight times short than a symbol length for a 15 kHz SCS in FR1.

In FR2 (mmW communications), directional beamforming are used b/w UE andgNB. As such, the UE and gNB communicate via beam pair link (BPL). Insome cases, the UE can detect beam failure (e.g. RSRP of BPL is bad),and send beam failure recovery request (BFRQ) to gNB. Such BFR processcan be cell-specific (e.g., there can be PCell BFR and SCell BFR).

As mentioned above, aspects of the present disclosure relate beamfailure detection and recovery. In some systems, narrow-beamtransmission and reception is useful for improving the link budget atmillimeter-wave (mmW) frequencies but may be susceptible to beamfailure. In mmW, direction beamforming is used between the UE and a BS,and the UE and BS communicate via a beam pair link (BPL). A beam failuregenerally refers to a scenario in which the quality of a beam fallsbelow a threshold, which may lead to radio link failure (RLF). NRsupports a lower layer signaling to recover from beam failure, referredto as beam recovery. For example, instead of initiating a cellreselection when a beam quality becomes too low, a beam pair reselectionwithin the cell may be performed.

FIG. 3 illustrates an example beam failure detection and recoveryprocedure, in accordance with certain aspects of the present disclosure.Beam failure may be detected by monitoring a beam failure detection(BFD) reference signal (RS) and assessing if a beam failure triggercondition has been met. As shown in FIG. 3, the UE 302 monitors, at 308,the BFD RS from the SCell 304. In some examples, beam failure detectionis triggered if an estimated block error rate (BLER) of referencesignals associated with a configured control resource set (CORESET) isabove a threshold (e.g., 10%). In some examples, the UE 302 detects beamfailure when the reference signal receive power (RSRP) of a BPL is belowa threshold.

To recover the SCell 304, the UE 302 can send a beam failure request(BFRQ) message on another cell. In some examples, the BFRQ is sent onthe PCell 306, as shown in FIG. 3. In NR systems, a two-step BFRQ may beused. The BFRQ may request a new transmission. As shown in FIG. 3, afterdetecting beam failure, the UE 302 sends the first step (or first stage)of the BFRQ at 310. The first step of the BFRQ message may include ascheduling request (SR) on the PCell 306. The SR may be sent ondedicated SR resources. The SR may request scheduling for the secondstep (or second stage) of the BFRQ message. As shown in FIG. 3, at 312,the UE 302 may receive a PDCCH from the PCell 306, in response to theSR, scheduling the second set of the BFRQ message. The UE 302 then sendsthe scheduled second step of the BFRQ message at 314 on the PCell 306.For example, the UE 302 sends a PUSCH including a MAC CE, as shown inFIG. 3. The MAC CE may include an index of the failed CC and a newrecovery beam candidate beam. In some examples, to find candidate newbeams, the UE may monitor a beam identification reference signal.

At 316, the PCell 306 responds to the BFRQ by transmitting a beamfailure recovery response (BFRR) message to the UE 302, as shown in FIG.3. The BFRR message may acknowledge the MAC CE and include an uplinkgrant scheduling a new transmission. For example, the uplink grant mayschedule a transmission for the same HARQ process as the PUSCH carryingthe MAC CE in the step two of the BFRQ. In some examples, the BFRR issent over a CORESET (e.g., referred to as a CORESET-BFR) the UE 302monitors for the response.

If the response is received successfully, the beam recovery is completedand a new BPL may be established. If the UE 302 cannot detect anyresponse within a specific time period, the UE 302 may perform aretransmission of the request. If the UE 302 cannot detect any responseafter a specified number of retransmissions, then the UE 302 may notifyhigher layers, potentially leading to RLF and cell reselection.

After receiving the BFRR, at 316, and before the new BPL is established,the UE 302 may communicate on the SCell 304 using a default beam.

Techniques and apparatus for the UE and BS (associated with the SCell)to determine when to apply the default beam are desirable.

Example High Reliability Transmission (Tx) Mode for 2-Step SCell BFR

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for performing beam failure recoveryinvolving a secondary cell. In some cases, one or more mechanisms may beutilized to increase reliability of a beam failure recovery (BFR)mechanism by implicitly providing higher priority for the recoverymessaging. Examples of such mechanisms include beam sweeping andrepetition.

As noted above, for secondary cell (SCell) beam failure detection, a BFRrequest (BFRQ) can be sent in a primary cell (PCell) physical uplinkcontrol channel (PUCCH) as a dedicated scheduling request, for example,according to the two-step BFRQ procedure is described above withreference to FIG. 3. Techniques described herein utilize one or moremechanisms to increase reliability of the BFR mechanism, for example,implicitly providing higher priority for the recovery messaging, forexample, for the medium access control (MAC) control element (CE) sentby the user equipment (UE) (e.g., which may include informationregarding the cell in which the beam failure was detected and/orindication of a new candidate beam).

FIG. 4 is a flow diagram illustrating example operations 400 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 400 may be performed, for example, byUE (e.g., such as a UE 120 a in the wireless communication network 100).Operations 400 may be implemented as software components that areexecuted and run on one or more processors (e.g., controller/processor280 of FIG. 2). Further, the transmission and reception of signals bythe UE in operations 500 may be enabled, for example, by one or moreantennas (e.g., antennas 252 of FIG. 2). In certain aspects, thetransmission and/or reception of signals by the UE may be implementedvia a bus interface of one or more processors (e.g.,controller/processor 280) obtaining and/or outputting signals.

The operations 400 may begin, at 402, by performing beam failuredetection (BFD) of a beam pair link (BPL) associated with a SCell incarrier aggregation (CA). At 404, the UE sends a BFRQ message to anothercell, the BFRQ message including an indication of a candidate recoverybeam for the SCell. At 406, the UE receives a message from the othercell. At 408, the UE sends a MAC CE after receiving the message, whereinthe MAC CE is sent using one or more mechanisms to enhance reliability.

FIG. 5 is a flow diagram illustrating example operations 500 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 500 may be performed, for example, bya BS (e.g., such as the BS 110 a in the wireless communication network100). The operations 500 may be complementary operations by the BS tothe operations 400 performed by the UE. Operations 500 may beimplemented as software components that are executed and run on one ormore processors (e.g., controller/processor 240 of FIG. 2). Further, thetransmission and reception of signals by the BS in operations 500 may beenabled, for example, by one or more antennas (e.g., antennas 234 ofFIG. 2). In certain aspects, the transmission and/or reception ofsignals by the BS may be implemented via a bus interface of one or moreprocessors (e.g., controller/processor 240) obtaining and/or outputtingsignals.

The operations 500 may begin, at 502, by receiving a BFRQ message from aUE, the BFRQ message indicating a beam failure detected in a SCell andincluding an indication of a candidate recovery beam for the SCell. At504, the network entity sends a message to the UE. At 506, the networkentity receives a MAC CE after sending the message, wherein the MAC CEis sent using one or more mechanisms to enhance reliability.

Operations 400 and 500 of FIGS. 4 and 5 may be understood with referenceto the call flow diagram of FIG. 6. As illustrated, after detecting abeam failure, the UE sends a BFRQ (e.g., a scheduling request in PCellor a PUCCH-BFR).

As illustrated in FIG. 6, in some cases, the response (e.g., a messagefrom the PCELL) after the UE transmits the PUCCH-BFR can be a normaluplink grant (e.g., with a cell radio network temporary identifier(C-RNTI) and/or a modulation and coding scheme (MCS) C-RNTI).

After receiving the response message from the PCell, the UE may transmitthe MAC CE (e.g., with information regarding the cell in which thefailure was detected and a candidate beam) using a high reliabilitytransmission (Tx) mode.

By transmitting the SCell BFR MAC CE with higher reliability (e.g., withbeam sweeping and/or repetition), the SCell BFR MAC CE may, in effect,have higher priority.

As illustrated, in some cases, the BFR MAC CE may be transmitted (e.g.,with beam sweeping and/or repetition) within a time window starting fromthe end of the PCell response. Within this time window, the UE cantransmit the MAC CE (e.g., in step 2 of the 2-step process) with apreviously known UL grant, which is either downlink control information(DCI) based (e.g., via the PCell response) or could be configured grant(CG) based (which generally refers to a grant of periodic uplinkresources).

In some cases, the UE may overwrite related uplink grant information totransmit the MAC CE, for example, based on a pre-configured highreliability Tx mode.

In some cases, the high reliability Tx mode can be based on apre-determined beam sweep pattern (e.g., the UE transmits the MAC CEmultiple times using different transmit beams according to the pattern).In some cases, the high reliability Tx mode can be a pre-determinedrepetition pattern (e.g., with an indicated beam given by originaluplink grant). The beam sweep pattern and/or repetition pattern could beconfigured (e.g., signaled via radio resource control (RRC), MAC CE, orDCI).

The duration of the time window (e.g., triggered/starting from the PCellresponse) duration can be a fixed value, for example, in terms of anumber of slots (e.g., ceil(N2/14)) slots. In some cases, the durationof the time window could be dynamically configured by a gNB.

EXAMPLE EMBODIMENTS

Embodiment 1: A method for wireless communication by a user equipment(UE), comprising performing beam failure detection (BFD) of a beam pairlink (BPL) associated with a secondary cell (SCell) in carrieraggregation (CA), sending a beam failure recovery request (BFRQ) messageto another cell, the BFRQ message including an indication of a candidaterecovery beam for the SCell, receiving a message from the other cell,and sending a media access control (MAC) control element (CE) afterreceiving the message, wherein the MAC CE is sent using one or moremechanisms to enhance reliability.

Embodiment 2: The method of Embodiment 1, wherein the message conveys agrant of resources for sending the MAC CE.

Embodiment 3: The method of Embodiment 1, wherein the one or moremechanisms comprise beam sweeping wherein the MAC CE is sent multipletimes with different transmit beams.

Embodiment 4: The method of Embodiment 3, wherein the different transmitbeams are defined by a beam sweep pattern.

Embodiment 5: The method of Embodiment 4, further comprising receivingsignaling indicating the beam sweep pattern.

Embodiment 6: The method of any of Embodiments 3-5, wherein the beamsweeping is performed within a time window triggered by reception of themessage from the other cell.

Embodiment 7: The method of Embodiment 6, wherein the time window isdynamically configured.

Embodiment 8: The method of any of Embodiments 1-7, wherein the one ormore mechanisms comprise sending the MAC CE with repetition.

Embodiment 9: The method of Embodiment 8, wherein the repetition isdefined by a repetition pattern and sent according to a beam indicatedin the message.

Embodiment 10: The method of Embodiment 9, further comprising receivingsignaling indicating the repetition pattern.

Embodiment 11: The method of Embodiment 10, wherein the repetition isperformed within a time window triggered by reception of the messagefrom the other cell.

Embodiment 12: The method of Embodiment 11, wherein the time window isdynamically configured.

Embodiment 13: The method of any of Embodiments 1-12, wherein themessage from the other cell comprises an uplink grant scrambled byC-RNTI or MCS-C-RNTI.

Embodiment 14: A method for wireless communication by a network entity,comprising receiving a BFRQ message from a UE, the BFRQ messageindicating a beam failure detected in a SCell and including anindication of a candidate recovery beam for the SCell, sending a messageto the UE, and receiving a MAC CE after sending the message, wherein theMAC CE is sent using one or more mechanisms to enhance reliability.

Embodiment 15: The method of Embodiment 14, wherein the message conveysa grant of resources for sending the MAC CE.

Embodiment 16: The method of Embodiment 14 or 15, wherein the one ormore mechanisms comprise beam sweeping wherein the MAC CE is sent by theUE multiple times with different transmit beams.

Embodiment 17: The method of Embodiment 16, wherein the differenttransmit beams are defined by a beam sweep pattern.

Embodiment 18: The method of Embodiment 17, further comprising providingsignaling to the UE indicating the beam sweep pattern.

Embodiment 19: The method of any of Embodiments 16-18, wherein the beamsweeping is performed within a time window triggered by reception of themessage.

Embodiment 20: The method of Embodiment 19, wherein the time window isdynamically configured by the network entity.

Embodiment 21: The method of any of Embodiments 14-20, wherein the oneor more mechanisms comprise sending the MAC CE with repetition.

Embodiment 22: The method of Embodiment 21, wherein the repetition isdefined by a repetition pattern and sent according to a beam indicatedin the message.

Embodiment 23: The method of Embodiment 22, further comprising providingsignaling to the UE indicating the repetition pattern.

Embodiment 24: The method of Embodiment 23, wherein the repetition isperformed within a time window triggered by reception of the message.

Embodiment 25: The method of Embodiment 24, wherein the time window isdynamically configured by the network entity.

Embodiment 26: The method of any of Embodiments 14-25, wherein themessage comprises an uplink grant scrambled by C-RNTI or MCS-C-RNTI.

Embodiment 27: An apparatus for wireless communication by a UE,comprising a memory and at least one processor coupled to the memory,the memory and the at least one processor being configured to performBFD of a BPL associated with a SCell in CA, send a BFRQ message toanother cell, the BFRQ message including an indication of a candidaterecovery beam for the SCell, receive a message from the other cell, andsend a MAC CE after receiving the message, wherein the MAC CE is sentusing one or more mechanisms to enhance reliability.

Embodiment 28: The apparatus of Embodiment 27, wherein the messageconveys a grant of resources for sending the MAC CE.

Embodiment 29: An apparatus for wireless communication by a UE,comprising a memory and at least one processor coupled to the memory,the memory and the at least one processor being configured to receive aBFRQ message from a UE, the BFRQ message indicating a beam failuredetected in a SCell and including an indication of a candidate recoverybeam for the SCell, send a message to the UE, and receive a MAC CE aftersending the message, wherein the MAC CE is sent using one or moremechanisms to enhance reliability.

Embodiment 30: The apparatus of Embodiment 29, wherein the messageconveys a grant of resources for sending the MAC CE.

Embodiment 31: An apparatus for wireless communication by a UE,comprising means for performing beam BFD of a BPL associated with aSCell in CA, means for sending a BFRQ message to another cell, the BFRQmessage including an indication of a candidate recovery beam for theSCell, means for receiving a message from the other cell, and means forsending a MAC CE after receiving the message, wherein the MAC CE is sentusing one or more mechanisms to enhance reliability.

Embodiment 32: A computer readable medium having instructions storedthereon for performing beam BFD of a BPL associated with a SCell in CA,sending a BFRQ message to another cell, the BFRQ message including anindication of a candidate recovery beam for the SCell, receiving amessage from the other cell, and sending a MAC CE after receiving themessage, wherein the MAC CE is sent using one or more mechanisms toenhance reliability.

Embodiment 33: An apparatus for wireless communication by a UE,comprising means for receiving a BFRQ message from a UE, the BFRQmessage indicating a beam failure detected in a SCell and including anindication of a candidate recovery beam for the SCell, means for sendinga message to the UE, and means for receiving a media access control MACCE after sending the message, wherein the MAC CE is sent using one ormore mechanisms to enhance reliability.

Embodiment 34: A computer readable medium having instructions storedthereon for receiving a BFRQ message from a UE, the BFRQ messageindicating a beam failure detected in a SCell and including anindication of a candidate recovery beam for the SCell, sending a messageto the UE, and receiving a media access control MAC CE after sending themessage, wherein the MAC CE is sent using one or more mechanisms toenhance reliability.

The techniques described herein may be used for various wirelesscommunication technologies, such as NR (e.g., 5G NR), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),time division synchronous code division multiple access (TD-SCDMA), andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). LTEand LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE,LTE-A and GSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). NR is an emerging wireless communications technologyunder development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB)and/or a NB subsystem serving this coverage area, depending on thecontext in which the term is used. In NR systems, the term “cell” andBS, next generation NodeB (gNB or gNodeB), access point (AP),distributed unit (DU), carrier, or transmission reception point (TRP)may be used interchangeably. A BS may provide communication coverage fora macro cell, a pico cell, a femto cell, and/or other types of cells. Amacro cell may cover a relatively large geographic area (e.g., severalkilometers in radius) and may allow unrestricted access by UEs withservice subscription. A pico cell may cover a relatively smallgeographic area and may allow unrestricted access by UEs with servicesubscription. A femto cell may cover a relatively small geographic area(e.g., a home) and may allow restricted access by UEs having anassociation with the femto cell (e.g., UEs in a Closed Subscriber Group(CSG), UEs for users in the home, etc.). A BS for a macro cell may bereferred to as a macro BS. A BS for a pico cell may be referred to as apico BS. ABS for a femto cell may be referred to as a femto BS or a homeBS.

A UE may also be referred to as a mobile station, a terminal, an accessterminal, a subscriber unit, a station, a Customer Premises Equipment(CPE), a cellular phone, a smart phone, a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet computer, a camera, a gaming device, a netbook, asmartbook, an ultrabook, an appliance, a medical device or medicalequipment, a biometric sensor/device, a wearable device such as a smartwatch, smart clothing, smart glasses, a smart wrist band, smart jewelry(e.g., a smart ring, a smart bracelet, etc.), an entertainment device(e.g., a music device, a video device, a satellite radio, etc.), avehicular component or sensor, a smart meter/sensor, industrialmanufacturing equipment, a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. Some UEs may be considered machine-type communication(MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include,for example, robots, drones, remote devices, sensors, meters, monitors,location tags, etc., that may communicate with a BS, another device(e.g., remote device), or some other entity. A wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as Internet or a cellular network) via a wired orwireless communication link. Some UEs may be consideredInternet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT)devices.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a BS) allocates resources for communicationamong some or all devices and equipment within its service area or cell.The scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. In someexamples, a UE may function as a scheduling entity and may scheduleresources for one or more subordinate entities (e.g., one or more otherUEs), and the other UEs may utilize the resources scheduled by the UEfor wireless communication. In some examples, a UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may communicate directly withone another in addition to communicating with a scheduling entity.

In some examples, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

The methods disclosed herein comprise one or more steps or actions forachieving the methods. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein, for example, instructions for performing the operationsdescribed herein and illustrated in FIG. 4 and/or FIG. 5.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1. A method for wireless communication by a user equipment (UE),comprising: performing beam failure detection (BFD) of a beam pair link(BPL) associated with a secondary cell (SCell) in carrier aggregation(CA); sending a beam failure recovery request (BFRQ) message to anothercell, the BFRQ message including an indication of a candidate recoverybeam for the SCell; receiving a message from the other cell; and sendinga media access control (MAC) control element (CE) after receiving themessage, wherein the MAC CE is sent using one or more mechanisms toenhance reliability.
 2. The method of claim 1, wherein the messageconveys a grant of resources for sending the MAC CE.
 3. The method ofclaim 1, wherein the one or more mechanisms comprise beam sweepingwherein the MAC CE is sent multiple times with different transmit beams.4. The method of claim 3, wherein the different transmit beams aredefined by a beam sweep pattern.
 5. The method of claim 4, furthercomprising receiving signaling indicating the beam sweep pattern.
 6. Themethod of claim 3, wherein the beam sweeping is performed within a timewindow triggered by reception of the message from the other cell.
 7. Themethod of claim 6, wherein the time window is dynamically configured. 8.The method of claim 1, wherein the one or more mechanisms comprisesending the MAC CE with repetition.
 9. The method of claim 8, whereinthe repetition is defined by a repetition pattern and sent according toa beam indicated in the message.
 10. The method of claim 9, furthercomprising receiving signaling indicating the repetition pattern. 11.The method of claim 10, wherein the repetition is performed within atime window triggered by reception of the message from the other cell.12. The method of claim 11, wherein the time window is dynamicallyconfigured.
 13. The method of claim 1, wherein the message from theother cell comprises an uplink grant scrambled by C-RNTI or MCS-C-RNTI.14. A method for wireless communication by a network entity, comprising:receiving a beam failure recovery request (BFRQ) message from a userequipment (UE), the BFRQ message indicating a beam failure detected in asecondary cell (SCell) and including an indication of a candidaterecovery beam for the SCell; sending a message to the UE; and receivinga media access control (MAC) control element (CE) after sending themessage, wherein the MAC CE is sent using one or more mechanisms toenhance reliability.
 15. The method of claim 14, wherein the messageconveys a grant of resources for sending the MAC CE.
 16. The method ofclaim 14, wherein the one or more mechanisms comprise beam sweepingwherein the MAC CE is sent by the UE multiple times with differenttransmit beams.
 17. The method of claim 16, wherein the differenttransmit beams are defined by a beam sweep pattern.
 18. The method ofclaim 17, further comprising providing signaling to the UE indicatingthe beam sweep pattern.
 19. The method of claim 16, wherein the beamsweeping is performed within a time window triggered by reception of themessage.
 20. The method of claim 19, wherein the time window isdynamically configured by the network entity.
 21. The method of claim14, wherein the one or more mechanisms comprise sending the MAC CE withrepetition.
 22. The method of claim 21, wherein the repetition isdefined by a repetition pattern and sent according to a beam indicatedin the message.
 23. The method of claim 22, further comprising providingsignaling to the UE indicating the repetition pattern.
 24. The method ofclaim 23, wherein the repetition is performed within a time windowtriggered by reception of the message.
 25. The method of claim 24,wherein the time window is dynamically configured by the network entity.26. The method of claim 14, wherein the message comprises an uplinkgrant scrambled by C-RNTI or MCS-C-RNTI.
 27. An apparatus for wirelesscommunication by a user equipment (UE), comprising: a memory and atleast one processor coupled to the memory, the memory and the at leastone processor being configured to: perform beam failure detection (BFD)of a beam pair link (BPL) associated with a secondary cell (SCell) incarrier aggregation (CA); send a beam failure recovery request (BFRQ)message to another cell, the BFRQ message including an indication of acandidate recovery beam for the SCell; receive a message from the othercell; and send a media access control (MAC) control element (CE) afterreceiving the message, wherein the MAC CE is sent using one or moremechanisms to enhance reliability.
 28. The apparatus of claim 27,wherein the message conveys a grant of resources for sending the MAC CE.29. An apparatus for wireless communication by a user equipment (UE),comprising: a memory and at least one processor coupled to the memory,the memory and the at least one processor being configured to: receive abeam failure recovery request (BFRQ) message from a user equipment (UE),the BFRQ message indicating a beam failure detected in a secondary cell(SCell) and including an indication of a candidate recovery beam for theSCell; send a message to the UE; and receive a media access control(MAC) control element (CE) after sending the message, wherein the MAC CEis sent using one or more mechanisms to enhance reliability.
 30. Theapparatus of claim 29, wherein the message conveys a grant of resourcesfor sending the MAC CE.